It is known in the art to utilize expansion bands for creating a water-tight seal between a gasket and a manhole opening in applications where the gasket is mounted in situ. For example, U.S. Pat. No. 4,387,900, assigned to the assignee of the present invention, discloses a gasket for use in an opening in manhole bases, which gasket is intended for in situ installation in manhole bases which have been precast in the factory or in which openings have been cored either at the factory or the job site. The gasket is comprised of an outer flange which is urged in an outward radial direction by an expansion band. The expansion band is clamped in the desired expanded position to place the gasket under compression and effect a fluid-tight seal between the gasket and the manhole base opening. The inner end of the gasket forms a water-tight seal about a pipe extending therethrough.
The clamping band described in U.S. Pat. No. 4,387,980 is plastic and is presized preparatory to delivery at the job site. A small insert portion, hingedly connected to one of the free ends of the clamping band, is moved into the gap between the free ends of the clamping band upon expansion thereof.
The disadvantages of such clamping bands reside in the fact that they are difficult to insert and that it is not possible to compensate for significant deviations in nominal diameter of the manhole opening. The latter problem is of the great concern in instances where openings are formed in the manhole by coring, the deviations in nominal diameter being caused, for example, due to the normal wearing of the coring equipment.
The expansion band of U.S. Pat. No. 4,387,900 has been improved by development of the expansion band described in U.S. Pat. No. 4,711,455 issued Dec. 8, 1987 and assigned to the assignee of the present invention. The hingedly mounted element of U.S. Pat. No. 4,387,900 is replaced by a plastic clamping band in which the free ends of the clamping band abut one another when the clamping band is expanded to the clamped position. This latter design also suffers from the same disadvantages of the clamping band in U.S. Pat. No. 4,387,900 in that the critical sizing problem remains unresolved.
Another solution to the problem has been developed as is disclosed in U.S. Pat. No. 4,746,127 in which a clamping band having an elongated slot at one end thereof and a cooperating projection slideably mounted within said slot enables the clamping band to be expanded, at which point an insert having a sawtooth configuration along one edge thereof is mounted within a transverse slot communicating with the first mentioned slot and cooperates with a similar saw tooth configuration along an associated engaging surface of said projection to lock the clamping band into the desired position. This structure has the disadvantage of requiring an additional, independant insert which must be inserted in place upon expansion of the band.
Still another improved method developed by the assignee of the present invention is described in copending application Ser. No. 174,076 filed Mar. 28, 1988, now U.S. Pat. No. 4,890,863 issued Jan. 2, 1990 and assigned to the assignee of the present invention. The clamping band of U.S. Pat. No. 4,890,863 is likewise provided with a separate, independant clamping member for maintaining the clamping band in the clamped position which either must be independantly tightened or must be inserted into the band upon expansion of the clamping band to the appropriate diameter.